Advances
in Non-contact displacement sensors bring new levels of quality
and efficiency to vehicle manufacturers.By Bryan
Manning and Robert Foster - Capacitec

Over the past
decade continued breakthroughs in sensor technology has improved
the automobile both inside and out. Most consumers are aware
of the benefits that sensors have contributed to automotive subsystem
improvements such as air bags, automatic braking systems (ABS)
and load leveling systems. Less obvious is the role sensors have
taken in the dramatic improvements in today's automobiles that
are a result of improved R & D, Quality Control and manufacturing
methods.

A major trend
in the Automotive market that is driving the requirement for
improved sensing is the fact that vehicle manufacturers are outsourcing
major subassemblies to so called Tier 1 suppliers. Today Tier
1 suppliers such as Robert Bosch, Delphi, Visteon and Continental
Teves are being given full design and manufacturing responsibility
for large subassemblies of the automobile. They now supply major
components such as complete suspensions, wheels/brakes or transmissions
to Toyota, DaimlerChrysler, GM, Ford, Volkswagen and other global
vehicle manufacturers. The role of the vehicle makers has also
changed over the years from one of a vertically integrated manufacturer
to the role they have today as major assembly houses.

This change at
the top has driven down to Tier 1 suppliers a more intense requirement
for R & D, Quality, and efficient manufacturing. This shift
in turn has dramatically increased the need for improved sensor
technology to meet the ever-increasing demands of these highly
specialized Tier 1 suppliers. They are now developing very specialized
state-of-the-art braking, drivetrain or suspension systems and
need specialized sensors to help in their research, design and
quality/efficient production processes. They are also subjected
to the very stringent quality system requirements such as Q1
and QA9000 placing constant emphasis on building quality parts
the first time, every time.

Capacitive non
contact displacement and thin gap sensors are good examples of
the type of sensors that have made significant contributions
to improving R & D, quality and manufacturing efficiencies
for vehicle manufacturers around the globe. The types of vehicles
that have been improved include automobiles, sports utility vehicles
(SUVs), light and heavy trucks as well as off-road vehicles.

As new Quality
Control methods such as In-process and 100% parts inspection
become more commonplace, displacement sensors are being used
in a greater number of locations throughout the automotive manufacturing
process. Non contact displacement sensors, in particular, are
more often the optimum choice in displacement sensors. This is
due to their many advantages such as the ability to handle 1000°C,
accuracy in the micron range, and small size. Additional benefits
will be outlined further in this article. Although there are
many determinants driving the increased demand for these sensors,
the benefits fall into the two major categories of improving
quality/performance and reducing cost.

Brought on by
global competition and more demanding end user customers, improved
quality continues to be a major theme for vehicle manufacturers
around the world. Manufacturers such as DaimlerChrysler, Ford
and Honda promote in their advertising that one of the best long-term
values that they can offer their customers is a consistent high
quality product. As technology progresses so too do the quality
methods employed. Older quality methods such as AQL are now consistently
being replaced with preferred methods such as 100% inspection
and zero defects. This change in philosophy requires displacement
sensor technology capable of measuring a new array of difficult
targets, locations and configurations.

The requirement
of increased precision measurement is another major factor in
today's quality control environment. Component and subassembly
dimensions are getting more and more precise. This is in turn
driving the need for increased precision in the measurement systems
controlling them. In many cases the components themselves are
becoming smaller requiring smaller and often more precise displacement
sensors. Automotive engineers now require sensors that can be
fit into locations with diameters of less than 1 mm. They also
need to measure gaps as small as 0.009" (0.23mm). Today
engineers are looking for displacement measurement systems that
can measure in millionths instead of tenths or measure 100 nanometers
instead of a micron.

In the R &
D departments of Vehicle Manufacturers and Tier 1 and Tier 2
suppliers, engineers are being forced by the marketplace to create
higher quality, longer mean time between failure (MTBF), better
performing, easier to manufacture components. Those involved
with engine components are also required to meet ever more stringent
government driven fuel efficiency and emissions requirements
such as the new Diesel Fuel Efficiency requirements enacted in
the United States in the year 2000.

The combined
growing demands from R & D, Quality and manufacturing methods
engineers has resulted in significant improvements in non contact
capacitive displacement technology at Capacitec over the past
decade.

These improvements
have allowed sensors to play a greater role in the labs and factory
floors of automotive manufactures from Porsche and BMW to Ford,
General Motors and Honda. Here are some specific examples of
where these technology breakthroughs have yielded the most added
benefits to vehicle makers:

1. Braking
Systems (Disc and Drum)

Beginning in the early 1990's Capacitec has developed a new line
of Disc Brake Wear Analysis Sensors. The new sensor system is
capable of taking high temperature 932°F (500°C) dynamic
brake system measurements both in the lab using dynamometers
and on-vehicle using rugged modular electronics. By measuring
displacement variables on a brake rotor in motion, data can be
collected and analyzed to show several characteristics such as:

Working with
OEMs such as Ford, Honda and Renault and
Brake suppliers such as Akebono, Allied Signal, Bosch and Federal
Mogul along with Brake Testing Houses such as Link Engineering,
we have continued to expand and enhance our capabilities.

Disc Brake
Wear Analysis Sensors

Figure 2
Displacement sensors can be placed in pairs on either side of
an automotive brake disc to dynamically monitor an assortment
of performance parameters.

The increased
demand for closer tolerances and rapid prototype designs has
forced automotive brake system and testing engineers to look
for new ways to verify engineering predictions and/or explain
the dynamic physical characteristics of braking system components.

Driven by Automotive
Manufacturers such as Ford, GM, Renault, Jaguar and Mitsubishi
along with Disc Braking Systems Suppliers such as Robert Bosch,
LUK, Akebono, Ferrodo, Teves and Federal Mogul as well as Testing
Laboratories in the US, Europe and Asia, Capacitec has developed
a new line of specialized non contact capacitive sensors. The
new model HPC-150-E-H sensor assembly combines the benefits of
small size and a high temperature 932°F (500°C) operation.

Another major
advantage of the new configuration is lower sensor replacement
cost. The redesigned sensor surface provides enhanced impact
survivability. In addition, an innovative new integral connector,
located behind the sensing surface, allows easy replacement of
coaxial extension cables without the added cost of replacing
the sensors themselves.

This new sensor
system is capable of taking dynamic brake system measurements
both on-vehicle at test track facilities as well as in Testing
Laboratories using dynamometers.

By measuring
the displacement data on a brake rotor in motion, measurements
can be collected and analyzed to show the following characteristics:

Drum Brake
Ovality Analysis Sensors

Figure 3
Two non-contact capacitive sensors work in tandem to measure
the ovality of the inside diameter of truck brake drums during
brake operation to detect deformations caused by extreme braking
conditions.

On large drum
braking systems such as those found on heavy trucks, manufacturers
are very concerned about the deformation of the brake drum during
high temperature and pressure situations. An example of where
these conditions exist is when brakes are applied for long periods
of time in high temperature environments. When the combination
of temperature and pressure is excessive the drums of these braking
systems become deformed. This could occur in emergency braking
situations or in prolonged downhill braking. In these cases the
drum changes from the normal round shape to an oval shape causing
potential malfunction of the braking system.

At Robert Bosch,
the measurement of this drum deformation required the development
of a custom on-board measurement system. The system consisted
of Capacitec model HPC-150 non-contact high temperature brake
probes installed to measure the changes in shape of the brake
drum. The sensor lead wires were routed through the wheel drums
and connected to special Capacitec Model 4200GP electronics bolted
to the outside circumference of the wheel. The electronics were
made to survive the high G forces incurred when the wheel rotated
at high speed.

The system was
successfully used to measure drum brake deformation during development
testing at a southwestern US desert proving ground. The ambient
temperature during the tests exceeded 120°F (49°C)

2. Powertrain
Systems

Vehicle manufacturers
are constantly researching improved designs and manufacturing
methods for engines and transmissions. This research requires
advanced displacement and gap sensors that have the following
characteristics:

Non contact measurement Ability to withstand high temperature/pressure No re-calibration due to variations
in types of metal Operation in oil or transmission
fluid Very small size to penetrate
inside tight spots Resistant to magnetic fields High frequency response to track
rapid rotation or axial movements

Capacitec sensors
thrive in these harsh and demanding environments. Here are some
specific examples:

Diesel fuel
injection systems

Cummins Engine
relies on Capacitec to solve a very difficult application for
the measurement of precise injection nozzle closure in their
diesel heavy truck engines. The final closure position of the
injection nozzle is very important for the efficient functioning
as well as noise maintenance of large engines. If the nozzle
is not closed enough there is a waste of fuel. If the nozzle
is too far closed it causes a "ringing" vibration that
leads to premature nozzle failure.

A particular
challenge in this application is the fact that the measurement
had to be taken in an environment of high magnetic field caused
by the very high magnetic generator coils. Adding to the challenge
was the very high-speed articulated motion of the nozzle stem,
which required a response of 30kHz.

Capacitec met
this challenge offering a model CMC60 sensor probe, which is
immune to magnetic fields and has a special matched magnetic
case. This sensor not only functioned perfectly under the high
magnetic field present but also did not jeopardize the strength
of the field that is powering the injector itself. The special
electronic package used to meet the high-speed requirement was
the Capacitec model 6100SC amplifier with 200kHz output.

The successful
solution from Capacitec allowed Cummins to produce diesel engines
that meet efficiency and the new Federal regulations on fuel
economy and emissions while at the same time reducing noise and
increasing mean time between failure (MTBF) for the engine.

Caterpillar Tractor
came to Capacitec with another very difficult problem that they
were facing. In long term testing of their engines they found
that carbon buildup could actually seize the piston rings allowing
oil to pass into the combustion chamber and causing emissions
problems. To solve this problem they needed to measure the motion
of a piston, which was cooled by oil. They therefor needed a
precise non-contact displacement sensor that could operate while
fully immersed in engine oil. The application also required embedding
a small sensor into the moving piston with the sensor monitoring
the up and down "flapping" motion of the rings operating
at the engine temperature of 482°F (250°C).

Capacitec met
the challenge again by installing very small diameter cylindrical
style sensors (4mm diameter) with special very thin diameter
coaxial cable (1mm diameter) that had to pass through a "grass
hopper link" assembly to be taken out through the oil pan
and then over to the on-board electronics. The solution also
required that the sensors operated with 100% immersion in engine
oil.

The Capacitec
solution allowed Caterpillar to produce engines that met the
new diesel emissions and fuel consumption guidelines, which began
in the year 2000 in the US.

Measurement
of 10 to 50 micron Piston ring movement

The companies
AVL List GmbH in Graz (Austria) and Federal Mogul in
Burscheid (Germany) have carried out a joint experiment to study
the
piston ring dynamics of a utility wagon diesel engine. They tracked
first and second piston ring axial motions by means of Capacitec
Model HPB-80 four-millimeter diameter capacitive probes placed
on either sides of each piston ring inside a reference piston.
In conjunction with complementary local pressure tracking they
were successful in gathering all necessary physical data that
were relevant to the understanding of the complex dynamics of
piston assembly. The aim of this study was to investigate the
possibilities of reducing the burn-off of engine oil. Reduction
of engine oil burn-off has important implications to user's costs,
the length of car service intervals and exhaust gas emissions
concerns.

Additional
Powertrain applications

Additional applications
where advanced Capacitec technology met customers' special demands
included the following:

Control of outer diameter of individual blades of a Honda Turbocharger
using 800°C probes and Model 6100 200kHz electronics package. Measurement of a rotating Turbocharger
for Allied Signal to measure radial runnout (Lissajous technique). Measurement of shaft motion at
the crankshaft bearing while entirely submersed in oil for Roush
Technologies racing division.

3. Vehicle
Assembly

Figure 5
Example of a contact type gap sensor for use in measuring exterior
gaps.

Exterior Surface
Gap Measurement

Consistent and
precise measurement of the various gaps around a vehicle's exterior
surface has proven to be quite a challenge for vehicle manufacturers
around the globe. This is a very difficult measurement problem
due to the fact that there are a wide variety of gap locations
each with differing requirements. Following is a partial list
of the variables to consider that exist in different gap locations:

Capacitec has
developed a number of products for this application based on
their experience in the Aircraft Industry. Smooth surfaces on
the exterior of an aircraft are crucial to assuring proper aerodynamics.
This in turn has an important effect on an aircraft's safety,
noise and fuel economy. The same issues found in aircraft assembly
are more and more prevalent in today's aerodynamic ground based
vehicle designs.

Based on their
experience with Airbus and Boeing, Capacitec developed a variety
of specialized contact and non-contact gap and flushness sensing
systems. Non contact gap sensors are used when both sides of
the target materials are conductive or where there is sensitivity
to finished surfaces such as the painted exterior of vehicles
at the end of the production line.
The contact sensor system is often the preferred solution when
the target material is non-conductive or has an unusual shape.

One example of
an exterior surface gap measurement application is the control
of flushness between a mounting bracket and the glass on a sunroof
for General Motors. Because the sunroof is curved, there is a
variation in the amount of glue required in different locations
between the sunroof glass and the sunroof bracket. The way the
process works is that the glass is first positioned into a fixture.
The fixture has Capacitec sensors mounted in eight locations
around the sunroof. The sensors control the amount of epoxy distributed
between the glass and bracket assuring a consistent geometry
to each sunroof.

By using the
Capacitec gap and flushness measurement system, General Motors
was able to achieve a ± 0.004" (100 micron) tolerance
on a gap of 0.060" (1.5mm). This in turn led to a sunroof
that was flush against the top of the vehicle dramatically reducing
noise while contributing to aerodynamics and fuel economy.

4. Automotive
Glass Production

The European
market leader in the supply of Automotive windshield and commercial
plate glass has been successfully using Capacitec non contact
displacement technology over the past 20 years to maximize the
throughput and quality of their high volume glass products.

In the automotive
application car windshields are manufactured in high volume 24
hours a day with very demanding environmental conditions. The
capacitive sensors control the tooling geometry as part of the
feedback loop to control parts quality of the windshields. The
sensors are exposed to 700°C in the high temperature glass
molding operation. They are also required to survive daily thermal
shock cycles from 25°C to 700°C. Laser technology sensors
were tried in the past but could not survive this high temperature
environment due to degradation of the cable fibers over time.

Advances in non-contact
displacement sensors are bringing new levels of quality and efficiency
to the research labs and assembly lines of vehicle manufacturers
worldwide.

From Brake Testing
Systems that survive the Mojave Desert test track to miniature
sensors that are exposed to the most severe temperature, pressure
and vibration environments, Capacitec sensors will enable automotive
engineers to continue designing safer, clearer and more efficient
vehicles into the next millennium. and beyond.